A conventional damping device is disclosed in U.S. Pat. No. 6,802,408 titled “Fluid Damper, Particularly For Movable Pieces Of Furniture” to Krammer, wherein the damper includes a piston composed of multiple ring disks located within an interior space of a cylinder, and at least two of the ring disks have a hole through which the damping fluid passes such that the piston moves in the interior space to reduce the speed of the movable pieces.
Besides, Taiwan Patent Nos. M327191, M327912, M329378, and M331331 also disclose damping devices and are referenced when the invention is made.